3D-Printed PEG–PLA/Gelatin Hydrogel: Characterization toward In Vitro Chondrocyte Redifferentiation

The advancement of 3D printing technology offers a sophisticated solution for tissue engineering and regenerative medicine. Several printable hydrogels have been developed with specific designs for certain tissues. However, there are few effective 3D-printed hydrogels for cartilage tissue engineering due to challenges with the hydrogel printability and the redifferentiation capacity of the articular chondrocytes on the hydrogel. This research study combined a PEG-PLA copolymer with gelatin to develop 3D-printed scaffolds for cartilage regeneration. Different hydrogel samples were prepared and studied regarding the effects of PLA chain length, gelatin content, and cross-linker concentration on the mechanical properties, swelling ability, and degradability of the hydrogels. An increase in the swelling ratio was observed, resulting in diminished compressive properties and accelerated degradation of the hydrogels with increased gelatin or decreased cross-linker and PLA chain length. Porcine articular chondrocytes were seeded onto the hydrogel scaffolds to assess cell adhesion, proliferation, and redifferentiation capability. Hydrogels with high swelling ability promoted the initial adhesion of cells on the scaffold, hence significantly increasing chondrocyte proliferation within 2 weeks of culture. Lowering the compressive modulus by increasing gelatin content improved chondrogenic redifferentiation. Glycosaminoglycan secretion was significantly enhanced when cells grew on hydrogels with greater amounts of gelatin. Furthermore, immunofluorescence staining of the cell-loaded hydrogels showed clusters of cells with a dense accumulation of a type II collagen network, a basis component of the cartilaginous matrix. Neither the PLA chain length nor the cross-linker amount affected chondrogenic function. The present study demonstrates that the PEG-PLA/gelatin hydrogels with increasing amounts of gelatin provide an optimal combination of swelling ratio, compressive modulus, and degradation rate, resulting in an appropriate environment to support the growth and redifferentiation of articular chondrocytes. This 3D-printed PEG-PLA/gelatin hydrogel will be useful for cartilage tissue engineering and possibly contribute to a new approach for cartilage defect treatment.